Tons of discussions on this here and elsewhere.
For the most part, its receiving rave reviews do to the inclusion of brushes for local edits.
I've been playing with the trial and I'm very pleased myself, I've switched from aperture to LR this past summer but given the additions, I'll be switching back.
I don't see adobe improving the organization of the images as much as apple has, i.e., Apple's DAM is superior and I also don't see LR having the same level of integration that aperture has. I can easily sync my iPhone, include the images in iWeb, and rapidweaver (A realmacsoftware product) and other apple products.
I've compared the RAW processing and while I will give an edge to LR on how it does stuff, I'm easily able to produce similar results. The brightness/contrast/recovery/blackpoint in LR seems to produce small difference then in aperture. nothing major just a difference in scaling.
I also like LR's grid view but Aperture's comes close and overall Aperture's UI and non-modal interface is much more preferred then the restrictive modal interface of Lr